820
J. Chem. Eng. Data 2008, 53, 820–825
Vapor–Liquid Equilibria for the Ternary System Ethanol + Water + 1-Ethyl-3-methylimidazolium Ethylsulfate and the Corresponding Binary Systems Containing the Ionic Liquid at 101.3 kPa Noelia Calvar, Begoña González, Elena Gómez, and Ángeles Domínguez* Chemical Engineering Department, Vigo University, 36310 Vigo, Spain
In this work, experimental data of isobaric vapor–liquid equilibria (VLE) for the ternary system ethanol + water + 1-ethyl-3-methylimidazolium ethylsulfate (EMISE) and for the corresponding binary systems containing the ionic liquid (ethanol + EMISE, water + EMISE) were carried out at 101.3 kPa. VLE data of binary systems were correlated using the e-NRTL and NRTL equations. With the obtained parameters, we can predict the behavior of the ternary system. In addition, the ternary system was correlated using the NRTL equation. A study of the evolution of the ethanol + water azeotrope composition with different amounts of ionic liquid was made.
Introduction Ionic liquids (ILs) are substances formed by ions, and they show a negligible vapor pressure at normal temperature and pressure conditions. This and other properties, such as their thermal stability and their capability as solvents, make the IL a new alternative for processes. The prediction of the most suitable IL for each separation process is limited since there is not enough information about the influence of the structure of the IL on its physical and solvent properties. Besides, experimental phase equilibrium data are required for developing thermodynamic (GE) models and for understanding their thermodynamic behavior. Vapor–liquid equilibria (VLE) data permit checking the potential of GE models which are used for the description of the nonideal behavior of systems containing IL. There have been some studies involving IL, where models such as the Margules equation, the Wilson equation, the NRTL equation, and the UNIQUAC equation have been used.1,2 In these works, it is stated that the NRTL equation gives the best empirical description of activity coefficients. Usually the model used to correlate the experimental data of systems containing ILs is the NRTL model.3 Although this model is theoretically developed for systems involving nonelectrolytes, it usually leads to good correlations for systems containing IL.4–8 Nevertheless, there is an extension of the NRTL model that considers the fact that ILs are organic salts that present ionic character, the e-NRTL model.9–11 This model has also been used in the literature,12,13 although it is less common. In any case, perhaps for the lack of models specifically created for systems with ILs and for its relative simplicity, the most used model is the NRTL model. In this work, experimental VLE for the binary systems ethanol (1) + EMISE (2) and water (1) + EMISE (2) and for the ternary system ethanol (1) + water (2) + EMISE (3) were carried out at 101.3 kPa. In addition, a comparison of the correlation models commonly used for the treatment of these experimental data, the NRTL and the e-NRTL models, was made. * To whom correspondence should be addressed. E-mail: admguez@ uvigo.es.
Table 1. Comparison of Measured Pure Component Properties Data with Literature Values at T ) 298.15 K F/g · cm-3
103η/Pa · s
component
exptl
lit.
exptl
lit.
ethanol water EMISE
0.78546 0.99705 1.23763
0.78546a 0.99705b 1.23915c 1.2296d
1.082 0.890 97.58
1.082a 0.890b 100.77c
a
From ref 16. b From ref 17. c From ref 18. d From ref 19.
Literature experimental data have been found for systems containing EMISE,4,14 but only the work of Arce et al. has comparable conditions.
Experimental Chemicals. Ethanol was purchased from Merck. It was degassed ultrasonically and dried over molecular sieves type 0.4 nm. Its purity was more than 99.8 %. Water was bidistilled and deionized. The IL used in this work was synthesized in our laboratory using the method described in a previous paper.15 To ensure its purity, NMR measurements were made. The water concentration (
